The present invention relates to a 2-cycle uni-flow internal combustion engine, in which a scavenging fluid which is air or a mixture of air and fuel and which has been pre-compressed in a crank chamber is introduced into a combustion chamber in a cylinder, and fuel is also supplied as required into the combustion chamber, the air-fuel mixture being then compressed by a piston and ignited by a spark so as to explode thereby producing output power, the combustion gas being then discharged as exhaust gas through one or more exhaust valves provided on the cylinder head.
Conventional 2-cycle spark-ignition internal combustion engines have their origin in a so-called three-port engine accomplished in 1891 by a British Engineer whose name is Day, J. In this type of engine, the air-fuel mixture supplied through a suction port provided in the wall of the cylinder is pre-compressed in the crank chamber and is supplied into the combustion chamber through a scavenging passage via a scavenging port provided in the portion of the cylinder wall on which the piston slides. The mixture is then compressed by the piston and is ignited by a spark so that the mixture explodes to produce power. After the combustion, the combustion gas is discharged as exhaust gas through an exhaust port provided in the portion of the wall of the cylinder on which the piston slides.
Several types of scavenging system have been proposed and used in this type of engine. For instance, a system so-called a loop scavenging system employs a scavenging port and an exhaust port which are arranged to diametrically oppose each other, while a projection provided on the head of the piston prevents the scavenging fluid from directly reaching the exhaust port. In a system known as a loop scavenging system, a plurality of scavenging ports are provided in symmetry on both sides of the exhaust port. Various combinations of these systems also are proposed. Although intense studies have been made with views to improve performance and fuel consumption in these systems, no further significant improvement seems to be attainable through such studies.
In general, ignitability of the mixture charged in the cylinders in the engines of the type described is inferior when compared with ordinary 4-cycle spark ignition engines due to the fact that the degree of dilution of the fresh mixture (mixture of air fuel) by the residual combustion gas is much greater than that in 4-cycle engines. This makes it difficult to operate 2-cycle engine with a lean mixture generally usable in 4-cycle engines. Namely, mis-fire tends to occur unless a specifically intense spark energy is supplied. Attempts for solving this problem in known 2-cycle engines have encountered with difficulty due to restriction from the scavenging system.
2-cycle engines also have various drawbacks such as large consumption of lubricating oil, as well as large amounts of emission of hydrocarbon and carbon monoxide attributable to conditions of scavenging and combustion peculiar in this type of engine. In addition, the exhaust gas has bad smell and contains smoke particles due to burning of lubricating oil introduced into the combustion chamber.
It is true that known 2-cycle engines have various advantages over 4-cycle engines of an equal engine displacement such as somewhat greater output power, simple construction and small size and weight, as well as lower production cost. Unfortunately, however, 2-cycle engines suffer from problems such as large rates of consumption of fuel and lubricating oil, possibility of environmental pollution due to nature of the exhaust gas, lack of stability and smoothness of operation, large vibration and noise, and so forth.
For these reasons, 2-cycle spark-ignition engines find only limited use in which advantages of this type of engine are fully enjoyed, e.g., small-sized portable agricultural machines, industrial machines, small motor bicycles, motor boats, and so forth. Thus, 2-cycle spark-ignition engines are excluded from uses where greater power is required as in the cases of automobiles, as well as uses where a demand exists for reduction in the noise level as in the cases of machines used in streets.
2-cycle uni-flow spark-ignition engines with overhead exhaust valve has been proposed in order to overcome the above-described problems. It has also been proposed to simplify this type of engine by eliminating valve actuating mechanisms.